ISSN: 2394 International Journal of Advanced Research … V-2-12-2.pdf · ISSN: 2394 International...
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International Journal of Advanced Research in ISSN: 2394-2819
Engineering Technology & Sciences December-2015 Volume 2, Issue-12
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Experimental Study and Behaviour of Encased Cold Formed Beam with
Triangular Corrugated Web
Stebin Mathe N.Parthasarathi
Department of Civil Engineering Assistant Professor
SRM University Department of Civil Engineering
Kattankulathur SRM University
Chennai Kattankulathu
Chennai
ABSTRACT: Whenever standard I-sections could not satisfy the moment carrying capacities, built-up I-sections have
been extensively used. In these built up sections it has been common practice to use more steel in webs
rather flanges. This results in uneconomical sections as steel is an expensive material. The introduction of
corrugated profile in web of I-sections consistently reduced the web instability and the application of
transverse stiffeners. But even after providing corrugated webs, effects like lateral torsional buckling
were observed. Thus measures are taken to reduce this buckling effect other than providing transverse
stiffeners and corrugated webs. Giving an encasement in the corrugated web beam could improve the
transverse deflections.The I-sections are encased with graded concrete mix not only improves resistance
to transverse deflections but also show a considerable increase in strength.
KEYWORDS: Corrugated steel webs, Concrete Encasement, Lateral Torsional Buckling, Shear
Strength, Cold Formed Steel Sections
1. INTRODUCTION:
Light gauge elements have been used for built-up beams and in case of heavy loads thickness of the web
plate required is more and also intermediate stiffener plates are to be used in case of heavy loads. The
light gauge steel members are defined as structural members cold formed to shapes in rolls or press
breaks from carbon or low alloy steel sheets or strips or flats, generally not thicker than 12.5mm. Due to
the heavy load materials used the dead load of the structure increases. To reduce this and improve the
structural efficiency, corrugated plates may be used.Corrugated profiles are introduced in order to achieve
adequate out-of plane stiffness and shear bulking without using stiffeners Therefore, further lateral
restraints have to be provided to control lateral buckling. But, lateral restraints cannot be further provided
in the form of steel stiffeners because of limitation in welding in corrugated web. Thus, corrugated web
encased with concrete can be used as an effective lateral restraint and further increasing load carrying
capacity of beam. Additionally, the concrete acts as cover for the web and improves the fire resistance of
the beam. The use of hot rolled sections become uneconomical for the steel structures subjected to light
and moderated loads, and for the structural members of short span lengths(e.g. joints, purlins, girts, roof
trusses).Thin sheet steel products are extensively used in building industry, and range from purlins to roof
sheeting and floor decking. Generally these are available for use as basic building elements for assembly
at site or prefabricated frames or panels. These thin steel sheets are cold-formed, i.e. their manufacturing
process involves forming steel sections in a cold state (i.e. without application of heat) from steel sheet of
uniform thickness. Sometimes they are also called light gauge steel sections or cold rolled steel
sections.Cold forming has the effect of increasing the yield strength of steel, the increase being the
consequence of cold working well into the strain-hardening range. These increases are predominant in
zones where the metal is bend by folding. The effect of cold working is thus to enhance the mean yield
stress by 15% - 30% for purposes of design, the yield stress may be regarded as having been enhanced by
a minimum of 15%.
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1.1.CORRUGATED WEBS:
A corrugated web beam is a built-up girder with thin walled corrugated webs and flange plates[1]
. The
profiling of the webs avoids the failure of the beam due to loss of stability before plastic limit loading of
the webs is reached. The primary characteristics of corrugated steel plates are negligible bending
capacity and adequate out of plane stiffness. To take advantage of these characteristics, the corrugated
steel plates have been considered an alternative to conventional concrete or steel girder webs. When used
as the web, the corrugated steel web carries the vertical shear. The flanges carry the moment due to
accordion effect. Engineers have long realized that the corrugations in webs enormously increase their
stability against buckling and can result in very economical design. Therefore, corrugated web beams
have the potential to eliminate many costly web stiffeners. In addition, the use of thinner webs result in
less raw material usage thus resulting cost savings estimated about 10-30% compared to conventional
built-up sections and more than 30 % compares to standard I-beams. Corrugations are of different types.
A triangular corrugated steel plate is composed of series of plane and inclined sub-panels.
In construction application, the webs usually bear the most compressive stress and transmit shear in the
beam while the flanges support the major external loads. Thus by using greater part of the material for
the flanges support the major external loads material saving can be achieved without weakening the load
carrying capacity of the beam. Nevertheless, as the compressive stresses in the web has exceeded the
critical point prior to the occurrence of the yielding, the flat web loses stability and deforms transversely.
This can be improved by using corrugated web, as an alternative to the plane web, which produces higher
stability and strength without additional stiffening and use of large thickness.
It has been found from earlier literature that when the beam length exceeds a given threshold value then
compression element that is the corrugated web becomes unstable and tends to buckle laterally even after
providing lateral stiffeners. Therefore, further lateral restraints have to be provided to control lateral
buckling. But, lateral restraints cannot be provided in the form of steel stiffeners because of the limitation
in welding in the corrugated web. Thus, corrugated web encased in concrete can be used as an effective
lateral restraint and further increasing the load carrying capacity of the beam. Additionally, the concrete
acts as a cover to web and improves the fire resistance of the beam
2. EXPERIMENTAL INVESTIGATION:
2.1.FABRICATION AND CASTING:
Cold formed steel plates of size 8 feet by 4 feet of 2 mm thickness were cut to desired dimensions by
using cutting machine. These plates were folded by using a press breaker machine with 450
corrugation
angle. After folding, the plates should be weld together in order to form an I-section. Flange plates are
placed at top and bottom and welded to the corrugated web[1]
. Figure 1 shows the welding procedure of
web to flange. Fabricated beams are placed in horizontal direction with web facing upwards.Figure 2
shows I-sections after welding and placed for concrete encasement. Concrete with grade M30 is mixed
and encased at both sides of the beam. The beams should left for 28 days of curing. Figure 3 shows
beams after being encased with M30 grade concrete.
Figure 1. Welding Of Plates
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Figure 2. Beams Placed For Casting
Figure3. Concrete Encased On Both Sides of Beam
2.2.TEST SET-UP:
All specimens are tested for flexural strength under two point loading by using vertical load frame
(reaction type)[6]
. The specimens were arranged with simply supported conditions, adjusted for a effective
span of 1.8 m (Figure 4). Loads were applied at one-third distance from the supported without shock,
increased at a uniform rate till the ultimate failure. Deflection of the beam was measured by three dial
gauges were placed one at mid span and two below point of loading. For each load increment the
deflection and crack were observed and tabulated.
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Figure 4. Test Set-Up
2.3.SPECIMEN DETAILS:
Total of six built-up cold formed I-sections are tested and studied. Two normal web I-sections of 2mm
thickness for both flanges and web are partially encased with M30 concrete with 150mm and 200mm
height. Four sections of triangular corrugated web profile with corrugation angle 450, thickness 2mm for
both flanges and web and of height 200mm and 150mm, also encased partially with M30 concrete on
both sides.
Top and bottom flange width bf -100 mm.
Thickness of the section (Flange and Web) tf -2mm.
Height of specimen -150 mm & 200 mm.
Span length – 2 m
The bonding between concrete and steel was expected to be provided by expansive nature of concrete.
Table 1 shows the beam designations.
Table 1: Beam Designation
Serial
No.
Beam
Designation Description
L/D
ratio
Number of
Specimens
1 ENB 150 Encased Normal Beam
Depth 150 mm 13.33 1
2 ENB 200 Encased Normal Beam
Depth 200 mm 10.00 1
3 EWB 150-I Encased Corrugated Web
Beam Depth 150 mm 13.33 1
4 EWB 150-II Encased Corrugated Web
Beam Depth 150 mm 13.33 1
5 EWB 200-I Encased Corrugated Web
Beam Depth 200 mm 10.00 1
6 EWB 200-II Encased Corrugated Web
Beam Depth 200 mm 10.00 1
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3. RESULTS AND DISCUSSION:
3.1.FLEXURE TEST:
All the specimens were tested for flexural strength under two point loading by using reaction type loading
frames. Deflection readings are observed from dial gauges and load readings were observed from load
indicator. The following observations were made during the progress of the tests. The observations are
summarized in Table 2.
Table 2. Ultimate Load And Deflection Of Specimens
Specimens Ultimate Load in KN
Max. Deflection at Mid-
Span in mm
ENWB 150MM 44.1 14.65
ECWB 150MM -I 61.3 25.36
ECWB 150 MM - II 58.8 24.56
ENWB 200 MM 66.2 14.2
ECWB 200MM -I 80.9 23.44
ECWB 200 MM - II 85.8 22.9
3.2.LOAD FACTOR:
Load factor is defined as the ratio of strength of built up section against standard section. In Table 3, the
flexural capacity of built up I section and the standard I section of same dimensions were compared.
From the results, it was observed that the Built up section with corrugated web has high flexural capacity
than that of standard I section. Flexure strength of the corrugated specimen is 1.39 times the strength of
standard section for H/t = 75 and for the aspect ratio 100, the load factor value is 1.29. From this, it is
understood that both values are greater than 1. Also aspect ratio increases as the load factor increases.
Table 3. Load Factor Values Of Specimens
Height of
specimen
Height to
thickness ratio
Ultimate load
(KN)
corrugated
web
Ultimate load
(KN) normal
web
Load factor
150mm 75 61.3 44.1 1.39
200mm 100 85.8 66.2 1.29
3.3.RESIDUAL STRENGTH OF BEAM:
The quantitative measure of residual strength of beam has been made with reference to the ultimate load.
The percentage difference of ultimate load for normally encased beam and encased corrugated web beam
gives a measure of residual strength (Table 4).
Table 4. Residual Strength Of Specimens
specimen Ultimate load (KN)
corrugated web
Ultimate load (KN)
normal web
Residual strength
in %
150mm 61.3 44.1 17.2
200mm 85.8 66.2 19.6
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Figure 5. Residual Strength of 150 mm And 200 mm Beams
3.4.STIFFNESS:
Stiffness may be defined as the load required causing unit deflection. The stiffness values of the specimen
at ultimate load were presented in the table. Table 5 shows that the stiffness value increases along with
the aspect ratio. Stiffness value of the specimen ENWB 200MM is higher of all the values, which shows
the specimen is stiffer than all other specimen. This may be due to the deflection of the specimen under
ultimate load which is lesser than all other specimen.
Table 5. Stiffness At Ultimate Loads
Specimens Ultimate Load in
kN
Max. Deflection at
Mid- Span in mm
Stiffness
KN/mm
ENWB 150MM 44.1 14.65 3.01
ECWB 150MM -I 61.3 25.36 2.417
ECWB 150 MM - II 58.8 24.56 2.394
ENWB 200 MM 66.2 14.2 4.66
ECWB 200MM -I 80.9 23.44 3.45
ECWB 200 MM - II 85.8 22.9 3.74
3.5. DUCTILITY:
The quantitative measure of ductility has to be with reference to the load-deflection response. Then, the
ratio of the ultimate deformation to the deformation at the beginning of the horizontal path (or, at first
„yield‟) can give a measure of ductility.
Table 6. Ductility values of specimens
Specimens Ductility
ENWB 150MM 5.86
ECWB 150MM -I 5.28
ECWB 150 MM - II 6.14
ENWB 200 MM 8.875
ECWB 200MM -I 11.72
ECWB 200 MM - II 12.05
17.2
19.6
16
17
18
19
20
150 mm 200 mm
Residual strength
Residual strength
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Figure 6. Ductility Values of Spicemen
3.6.LOAD – DEFLECTION GRAPHS:
The dial gauges were used to measure deflection for the specimens at mid-span and one-third of the span
length. The obtained deflections were plotted against their corresponding load values obtained from the
experimental results[6]
. All the load deflection curve shows an increase in the load deflection which varies
linearly up to the Ultimate value. The maximum deflection occurs in mid-span. The plots also show that,
for 150mm depth beams, the encased corrugated section ultimate load carrying capacities are higher than
encased normal web beam and for 200mm depth beams , the encased corrugated section ultimate load
carrying capacities are againhigher than that of encased normal web beam.
Figure 7. Load-Deflection Curve of 150mm Beam
5.865.28
6.14
8.875
11.72 12.05
0
2
4
6
8
10
12
14
ENWB 150MM
ECWB 150MM -I
ECWB 150 MM - II
ENWB 200 MM
ECWB 200MM -I
ECWB 200 MM - II
Ductility Index
Ductility Index
0
5
10
15
20
25
30
0 10 20 30 40 50 60 70
Defl
ecti
on
in
mm
load in KN
150 MM BEAM
ECWB-I
ENWB
ECWB-II
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Figure 8. Load-Deflection Curve of 200mm Beam
3.7.COMPARISON OF ULTIMATE LOADS:
Figure 9. Comparison of Ultimate Loads
3.8.COMPARISON OF MAXIMUM DEFLECTIONS:
Figure10. Comparison of Maximum Deflections
-5
0
5
10
15
20
25
0 20 40 60 80 100
Defl
ecti
on
in
mm
Load in KN
200 MM BEAM
ENWB
ECWB-II
ECWB-I
44.1
61.3 58.866.2
80.985.8
0
10
20
30
40
50
60
70
80
90
100
ENWB ECWB-I ECWB-II
ULTIMATE LOADS 150MM
ULTIMATE LOADS 200MM
14.65
25.36 24.56
14.2
23.44 22.9
0
5
10
15
20
25
30
ENWB ECWB-I ECWB-II
MAXIMUM DEFLECTION-150MM
MAXIMUM DEFLECTION-200MM
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3.9.MODES OF FAILURE:
From the results obtained the failure modes of different specimens were discussed. The failure was
typically in the form of flexural cracks originating from the bottom of the specimen and extending
towards the top of the specimen. Majority of cracks were formed between two point loading and some at
the end supports. Failure pattern of encased normal beam and encased corrugated beam doesn‟t have
much difference. But the load carrying capacities of encased corrugated beam is comparatively higher
than that of normal encased beam. The buckling of flange in outward direction was observed due to the
loss strength in spot welding between web and flange.
Figure 11. Failure Pattern of ENWB-200mm
4. CONCLUSION AND FUTURE SCOPE:
Cold-formed sections with concrete have resulted in increased resistance to lateral-torsional buckling..
For 150mm depth beams, the ultimate load carrying capacity of encased cold-formed corrugated web
beams 25-30% higher than encased normal web beams. For 200mm depth beams , the ultimate load
carrying capacity of encased cold-formed corrugated web beams is about 20-25% higher than that of
encased normal web beam. The maximum deflection of encased cold-formed corrugated beams was 40-
50% higher than encased normal beams. The ductility of the specimens are more than 5 thus can be used
in earthquake-prone areas. For future research, the corrugation type can be changed and also special
concrete can be used instead of conventional concrete.
REFERENCES: 1. Elgaaly, Anand Seshadri,(1998) “Depicting the Behaviour of Giders with corrugated Webs up to Failure using Non Finite
Element Analysis” , Advances in Engineering software, Vol.29, No.3-6,pp 195- 208
2. Ezzeldin Yazeed Sayed(1998) “Ahmed Lateral Torsion-Flexure buckling of Corrugated Web Steel Girders”. The
Institution of Civil Engineers Structures and Buildings, Vol.39, No.3-6,pp 195- 208
3. Hassan H.Abbas, and Robert G.Driver(2007) “Simplified analysis of flange transverse bending of corrugated Web Girders
under In-Plane Moment and Shear”. Engineering Structures, Vol.29 , pp 2816-2824
4. Jiho Moon, Jong-Won Yi(2009) “Lateral Torsional Buckling of I-Girder with Corrugated Webs Under Uniform
Bending”,Thin-Walled Structure , Vol.47, pp 21-30
5. Kazemi nia korrani, (2009) “Lateral Bracing of I-Girder with Corrugated Webs Under Uniform Bending”, Journal Of
Constructional Steel Research, Vol.66, pp. 1502- 1509
6. Khalid and Sahari(2004) “Bending Behavior of Corrugated Web Beams”. Journal of Materials Processing Technology,
Vol. 150 Pg. 242- 254.